We propose to study molecular, genetic and histologic markers of breast cancer risk in women with benign breast disease. We will use a unique cohort of such women to pursue the following Specific Aims: 1. To determine the effects on breast cancer risk of the 6A polymorphism of the transforming growth factor beta type I receptor (T(3R-I). We will also study how expression levels of the TpR-l, and its principal substrate Smad2, affect breast cancer risk in women with proliferative breast lesions. 2. To evaluate the combined influence on breast cancer risk of benign breast lesions and 424 single nucleotide polymorphisms (SNPs) from 86 candidate genes involved in estrogen biosynthesis, function and oxidative metabolism. Cross-sectional analyses will also be performed that examine how specific genotypes are correlated with different types of benign breast disease. These studies will explore potential influences on breast cancer risk of ER-mediated cell proliferation or the generation of oxidative estrogen metabolites that may damage DNA. 3. To expand the size and length of follow-up of our study cohort. The research will be based on a large retrospective cohort study of women who underwent benign breast biopsy between 1954 and 1995. Paraffin-embedded tissue from the entry biopsy of these patients is available. By the end of this project we estimate that we will have observed 890 breast cancer cases during follow-up among the 11,547 members of this cohort. We will conduct a series of nested case- control studies on these women. The 890 breast cancer cases will be matched by race, age and year of their benign breast biopsy to 1780 controls (1:2 ratio). Genotyping will be performed using the Illumina GoldenGate assay while immunohistochemical methods will be used to identify abnormal protein expression. We will use supervised principal component analyses to assess the individual and combined effects of molecular, histologic and epidemiologic variables on breast cancer risk. A false discovery rate (FDR) approach will be used to identify promising findings that will be subject to validation in other data sets. This project takes advantage of an established cohort of women with biopsy-confirmed benign breast disease. Clinical, demographic, and histologic information, as well as genomic DNA is uniformly available. This project will permit the combination of modern methods in molecular biology, genetics, pathology and epidemiology to assess potentially powerful new markers of breast cancer progression and prognosis. We expect that it will lead to important advances in the prevention and treatment of this disease.